Blade CP Tail Motor Fix

The details of how we developed this fix as well as other solutions we are working on can be found on our Blade CP Tail Motor page. Be sure to read about the limitations at the bottom of this page as well.

Pulse Width Modulation With Original Setup (3 cell li-po) Pulse Width Modulation With Zener Diode And Resister (3 cell li-po)

We sell a plug-in and solder on version as well as the bare components. The plug-in doesn't require any soldering on your part, you just plug it into your 4-1 and plug your tail motor into it. Solder joints have heat shrink tubing covering them. This version has the advantage that you can easily swap it in or out. The solder on version is exactly the same, but without any plugs. Finally the components are just the zener diode and resistor. The details of how to make your own are shown further down the page. If you want to order one from us, email us. Our Prices plug-in version $14.99 plus $5.99 shipping and handling solder version $9.99 plus $5.99 shipping and handling components only $5.99 plus $5.99 shipping and handling

Items Required: 9.1 V 5 W Zener Diode 2.2 Ω 1 W Resister Soldering Iron and Solder Electrical Know How Soldering Skills Optional Items: Additional wiring Heat shrink tubing Additional connectors

If you are not confident in your soldering skills or electrical know how, do not try to do this yourself. This hobby is blessed with many people that are more than willing to help you, if you do not know what you are doing, don't try this. We assume no liability for any outcome relating to this.

Now that we got the disclaimer out of the way (stupid lawyers), let's move on... The circuit diagram for this modification is shown below: You can implement this circuit in a number of ways, first we'll go over the quick and easy method

Quick and Easy Method Determine which wire is negative and positive coming out of the 4-1. If you have the standard setup with reverse switches set as outlined in the manual, the upper tail motor pin on the 4-1 is postive and the lower tail motor pin on the 4-1 is negative. Check that the tail plug has the red wire upward and that the reverse switch is in the right spot. Double check it. If you get this wrong, you could ruin your 4-1. With battery unplugged, use a soldering iron to remove the positive wire from the tail motor (should be red as long as reverse switch is set as outlined in the manual and the tail motor plug has red upward and black downward in 4-1). Solder the anode of the zener diode to the tail motor where the black wire is still connected (should be black as long as reverse switch is set as outlined in the manual and the tail motor plug has red upward and black downward in 4-1). A zener diode has an anode side and a cathode side, the cathode side is marked with a line. At this point the black wire and anode end of the zener diode should be soldered to the tail motor. If you mess up and solder the cathode end to the negative output of the 4-1, you could ruin your 4-1. Solder one end of the resister to the positive wire (should be red as long as reverse switch is set as outlined in the manual and the tail motor plug has red upward and black downward in 4-1). Now solder the cathode of the zener diode and the other end of the resister to the remaining motor contact (all three together). Your done!

Other Installs You can also install the components following the circuit diagram near the 4-1 using additional wires/connectors. You need to be sure the diode and resistor can dissipate some heat or they will fail. Our plug-in install puts the diode and resistor towards the rear of the main body.

Limitations The two components used in this modification, the zener diode and resister, typically will always fail into a open circuit condition. If the zener diode fails you will simply lose the voltage protection it was providing, helicopter flight will be not be affected significantly. If the resister fails, the motor will stop spinning and you will lose tail control; however, this never occured in any of the flight testing we did and we were using resisters with 1/4 the power rating (.25 W compared to 1.0 W resistors). This is basically a common zener regulated power supply. In general these circuits are designed so that if the load (tail motor) is completely removed, nothing will fail. To get optimal performance, we couldn't protect against this possibility. As a result, if the motor is not connected the diode will fail. The 4-1 can put of a max of 11.1 V constantly, since the zener diode is 9.1 V and 5 W, that means the max current the zener diode can handle is 5 W / 9.1 V = .549 A. Since the voltage drop across the resistor is 2 V (11.1 V - 9.1 V), that means the resistor size required is 2 V / .549 A = 3.64 Ω however, since all the current goes through the resistor, a resistance this large results in poor performance of the tail motor. If you consider the circuit only when the tail motor is present, you can decrease the size of the resister; however, if you get too low the diode will fail. Also, since all the current goes through the resister, as you raise the resistance you decrease the power to the motor and increase the power the resistor must dissipate. As a result, optimal performance is achieved with the lowest resistance that prevents damage to the diode. If you increase the resistance, the resister has to dissipate more heat and failure becomes more likely. In our flight testing we used a 9.1 V 5 W zener diode and a 2.2 Ω .25 W resister. We used this small resister to see if it would fail. After normal flying it doesn't seem to heat up at all and we never saw a failure with this setup; however, when we held onto the helicopter and gave it full right rudder at full throttle, the resister would start to heat up after about 5 seconds. Remember, this is with the .25 W resister, we now use a 1 W resister which can handle a lot more current. Although we have never seen one fail, we do think that if you apply full throttle and full right rudder for a long time, the resister may fail. As far as damaging the 4-1 if you connect the zener diode backwards, this would basically put a 2.2 Ω resister across it. Which, at full throttle would pull 5.045 A out out the 4-1, at lower throttles this value would be less. As a result, damage is not guaranteed if this did occur, but it isn't something we've ever tried (or recommend trying).